The portion of I-75 from Tampa northward was a part of the original 1955 Interstate Highway plans, with I-75's southern terminus at I-4's current western terminus. Planning to extend the interstate south to Miami began in 1968 after massive growth in Southwest Florida, which resulted in I-75 being realigned to travel on the eastern fringes of the Tampa Bay area, and the last portion of the highway was opened in 1993.

For FDOT inventory purposes, it is designated as State Road 93 (SR 93) for most of its length in Florida (with exception to the Tampa Bay area, where SR 93 follows I-275, while SR 93A travels with I-75 in the latter's bypass of the area).

At the junction of SR 869 (Sawgrass Expressway) and I-595, I-75 (while maintaining its south–north status) enters a west–east trajectory as it crosses the Everglades by way of Alligator Alley, a toll road that runs from the Collier Boulevard (Exit 101) toll plaza to the US-27 toll plaza (Exit 23). It was originally constructed as a two-lane highway before it was converted to a four-lane highway meeting Interstate Highway standards. At this point, I-75 loses a lane in each direction, heading west, losing another lane west of the U.S. Route 27 (US 27) interchange.

The Alligator Alley section west of Fort Lauderdale, Florida and east of Naples is due west–east and is one of only two sections of I-75 that are tolled (the other is the Mackinac Bridge). There are only two interchanges along the 75 mile tolled portion of Alligator Alley in addition to two rest areas and a number of scenic outlook points as it crosses the Florida Everglades. I-75 enters Collier County along Alligator Alley just west of the Snake Road exit (exit 49) and passes through the Big Cypress National Preserve between the Collier County border and State Road 29 (exit 80). There are a number of small bridges along Alligator Alley to allow wildlife to pass under the freeway especially along the Florida Panther National Wildlife Refuge east of SR 29. Extensive fencing also prevents wildlife from crossing traffic.[4]

At the Hillsborough–Pasco county line (south of SR 56 (Exit 275)), I-275 rejoins I-75 (at Exit 274, southbound only) and I-75 changes into a southwest–northeast trajectory as it passes through Pasco, Hernando, and Sumter Counties where it runs through parts of the Withlacoochee State Forest on its way to the junction with Florida's Turnpike. Widened median segments exist in Northern Pasco County, Hernando County, and in Sumter County north of County Road 476-B (Exit 309). Some of these median segments are actually considered part of the Withlacoochee State Forest itself. The Withlacoochee State Trail runs beneath I-75 between US 98/SR 50 (Exit 301) and the Hernando–Sumter County line, where it also crosses over the Withlacoochee River. All of Interstate 75 from the Georgia border to Tampa, Florida is three lanes in each direction, unless closed for construction. This is to accommodate for the immense number of tourists and vacationers that come to Florida.

The Cross Florida Greenway bridge over I-75

After Florida's Turnpike (accessible from southbound I-75 only), I-75 changes into a general southeast–northwest trajectory, which is sustained to the Georgia state line and beyond. I-75 passes beneath the Cross Florida Greenway, which contains a land bridge built across the highway in 2001 between Exits 341 and 350,[6] before entering the City of Ocala, and passing by the cities of Gainesville and Lake City and crosses I-10 at an interchange before entering the state of Georgia, near Valdosta.

Construction of the original route from the Georgia border to Tampa via Gainesville and Ocala lasted through most of the 1960s. The first segment of I-75 to open in Florida was from the Georgia border to State Road 6 just south of Jennings, which opened in 1963. It would reach U.S. 90 in Lake City later that year. By mid-1964, I-75 opened from Lake City to the newly completed Florida Turnpike (known then as the Sunshine State Parkway) in Wildwood. Segments of the original route that are now part of I-275 near Tampa would begin opening in 1966, and construction of the full route would be completed by 1969.[8]

Due to major growth in Southwest Florida (particularly Fort Myers and Naples), it was becoming clear that this part of the state would soon need a freeway. Florida's state government first proposed to build a West Coast Turnpike in 1964 from the Tampa Bay area south to Naples.[9] Plans for the West Coast Turnpike (which would have been tolled) were cancelled in 1968, when it was announced that U.S. Secretary of Transportation Alan Boyd had approved an extension of I-75 south to Naples and then east to Miami. The Federal Government would pay for 90% of the extension using funds allocated by the Federal-Aid Highway Act of 1968, which was signed into law by President Lyndon B. Johnson.[10][11]

In preparation for the extension, I-75's designation was extended along the pre-existing route of I-4 over the Howard Frankland Bridge into St. Petersburg by the end of 1969 (I-4's designation would be truncated to its current terminus at this time). From St. Petersburg, I-75 was proposed to continue south over the Sunshine Skyway Bridge and continue south along a new freeway roughly parallel to the Tamiami Trail (U.S. 41) along the lower Gulf Coast to Naples.

I-75E shield

As the extension was planned in 1968, plans were also made for a freeway bypassing Tampa Bay to the east. The bypass was initially planned to be designated I-75E, and was to split from I-75 near Wesley Chapel and rejoin it just north of Ellenton. However, in 1972, it was determined that maintaining the main route of I-75 through Downtown Tampa would eventually require major improvements to the existing infrastructure to handle through traffic. As a result, it was decided that I-75 would instead follow the bypass route, with the original route through downtown Tampa and St. Petersburg becoming I-275. I-75 reached as far south as 38th Avenue North in St. Petersburg when the designations were switched. Despite the designation switch, both freeway's hidden designations still reflect the originally planned routing, with I-75's SR 93 designation following I-275, and the current route of I-75 on the bypass being designated SR 93A.[12] Construction on the bypass segment of I-75 began in 1979.[8]

Due to environmental concerns of upgrading the Tamiami Trail (which runs along the northern border of Everglades National Park) and the fact that the Dolphin Expressway was not built to Interstate standards, the decision was made in 1973 to shift I-75's proposed route to cross the Everglades along Alligator Alley. By using this route, I-75 would run along the alley to the proposed Port Everglades Expressway, where it would turn south along a new freeway through the western suburbs of Weston and Pembroke Pines to Miami. It was still planned to continue east to I-95, but due to local opposition, I-75 was not built past its current terminus at SR 826 (Palmetto Expressway) in Hialeah. With this new route, the Port Everglades Expressway was then planned to be built as an interstate highway designated I-595 to provide an interstate connection between I-75 and I-95.

The first piece of the south extension of I-75 to open was a short segment just east of Fort Myers from SR 78 south to Corkscrew Road in 1979. This piece would extend north to Tucker's Grade just south of Punta Gorda in early 1980 and south to Immokalee Road in North Naples by 1981. Also in 1981, the segment from U.S. 301 in Manatee County south to River Road near Venice opened, which would be completed south to the southern segment in Punta Gorda later that year. It would reach Alligator Alley in Naples by 1984. The route from Tampa to Naples would be complete by 1986 as segments of the Tampa bypass were opened from 1982 to 1986. In the Miami area, I-75 was opened from U.S. 27 to its terminus at the Palmetto Expressway in 1986.[8]

The Florida Department of Transportation transitioned existing interchange exit numbers on all Interstate highways from sequential exits to mileage-based exits in January 2002.[13]

Looking east at Alligator Alley from recreation area and rest stop at I-75 and Miami Canal

The Alligator Alley segment (from Naples to just west of Fort Lauderdale) previously existed as a two-lane tollway connecting the two coasts of Florida. Initially known as Everglades Parkway (State Road 84), it opened for traffic on February 11, 1968, after four years of construction. Built by H. L. Mills Construction Company, it had been called the most controversial roadway ever built in Florida during its initial construction.[14] The name "Alligator Alley" was given by the American Automobile Association while it was planned since they believed it would be useless to cars, merely an "alley for alligators". However, as alligators often frequent the waterways beside the road, and occasionally the road itself, the nickname has developed a somewhat literal meaning. The state would officially adopt the Alligator Alley name in 1966.[14]

As a two-lane road, Alligator Alley suffered from poor construction and environmental planning. It was also notorious for high-speed accidents with both head-on collisions and collisions with wildlife. The need to improve it was one of the factors in the decision to reroute I-75 onto the alley, which was rebuilt as a four-lane interstate highway between 1986 and 1992. Many bridges and culverts designed to let water and wildlife pass underneath and permit the natural water flow of the Everglades were built as part of the upgrade.[15] This helped to reduce the environmental impact of the highway somewhat, especially upon the severely endangeredFlorida panther. The completion of the converted Alligator Alley was the final link of the I-75 extension. The segment was signed Interstate 75 on November 25, 1992, fully completing the highway from Miami to Sault Ste. Marie, Michigan.[16]

In January 2000, the west end toll plaza of Alligator Alley was dedicated to the memory of Edward J. Beck, a toll taker who was murdered while on the job on January 30, 1974.[17]

A state effort to privatize Alligator Alley failed in May 2009 when no bids were received for the highway that met the required terms.[18]

Many widening projects are underway on I-75 to eventually bring it to at least six lanes from Naples to the Georgia state line.[22][23][24]

FDOT is implementing express lanes along 28 miles (45 km) of the I-75 and SR 826 (Palmetto Expressway) corridors, from just south of the SR 836 (Dolphin Expressway), in Miami-Dade County, to I-595 in Broward County. This project will complete another section of the South Florida managed lanes network for all motorists and will improve mobility, relieve congestion, provide additional travel options and accommodate future growth in the area. The 75 Express Lanes project extends 15 miles (24 km) along I-75 from Northwest 170 Street, in Miami-Dade County, to I-595, in Broward County. Work will be completed in four segments to minimize affects to the public. Construction began early 2014 and is scheduled to be completed by mid-2019. The total project is estimated to cost $481 million.[25]

Several rest area facilities exist along I-75 throughout the state. In addition, there are separate facilities for each direction of the Interstate in Hamilton and Suwannee counties, southbound and northbound, respectively, and a welcome center south of the state line. Exit 131 has a single facility accessible from both travel directions on I-75, as well as the intersecting highway. Exit 161 had a rest stop at the interchange's southeast quadrant but it closed in 2015 because of low usage.[26] Exit 191 also had a rest stop at the interchange's northeast quadrant that closed in the 1990s.[27] Each rest area has rest rooms, vending machines, picnic tables, dog walk areas, and nighttime security. The welcome center also has travel information and free orange juice, the state's official state beverage.[28]

Motorist-aid call boxes were installed starting in 1973, initially from the Georgia line to Lake City,[29] eventually being installed on both outside shoulders of the road every one mile (1.6 km) to allow drivers to indicate the need for gasoline, repair (tire or engine), or emergency services (police, ambulance, or fire). The majority of the call boxes were removed in late 2013 because of the rising maintenance cost and the availability of newer technology.[30]

Intelligent transportation systems (ITS) are used throughout the Interstate. ITS is a fiber optic system of traffic cameras, overhead message signs, microwave vehicle detectors, travel time sensors, road and weather information sensors, and highway advisory radios.[30] FDOT has a data-share agreement with Waze which provides real-time information for the state's 5-1-1 service, ITS, and to Waze users.[31]